Subject: [PATCH] profiles: emacs-subdirs: Avoid building list with a loop

From: Thiago Jung Bauermann <[email-masked]>
Date: Fri, 24 Jan 2025 20:01:35 -0300

If the EMACSNATIVELOADPATH environment variable (by mistake) has duplicated
paths, Emacs fails to load with:

  $ emacs
  List contains a loop:
  ("/home/user/.guix-profile/lib/emacs/native-site-lisp"
   "/gnu/store/…-emacs-lsp-mode-9.0.0/lib/emacs/native-site-lisp"
   "/home/user/.guix-profile/lib/emacs/native-site-lisp"
   "/home/user/.guix-profile/lib/emacs/native-site-lisp"
   "/gnu/store/…-emacs-lsp-mode-9.0.0/lib/emacs/native-site-lisp" . #2)
  $ echo $?
  255

A git bisect in Guix to find when the problem was introduced arrived at
commit e9b13294700d ("profiles: emacs-subdirs: Also expand
native-comp-eln-load-path.").

Fix the problem by applying Liliana's suggestion of changing 'nconc' to
'append' in the Elisp code written to subdirs.el.

* guix/profiles.scm (emacs-subdirs): Use 'append' rather than 'nconc'.

Change-Id: If646b806f24666b5247850d30d2819c7482c130b
Fixes: <https://issues.guix.gnu.org/75709>
Suggested-by: Liliana Marie Prikler <[email-masked]>
---
 guix/profiles.scm | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/guix/profiles.scm b/guix/profiles.scm
index 87b9543ac01f..63b2a08a48d4 100644
--- a/guix/profiles.scm
+++ b/guix/profiles.scm
@@ -1230,8 +1230,8 @@ (define build
                         (setq native-comp-eln-load-path
                               (mapcan (lambda (dir)
                                         (if (equal dir needle)
-                                            (nconc ',native-comp-dirs
-                                                   (list dir))
+                                            (append ',native-comp-dirs
+                                                    (list dir))
                                             (list dir)))
                                       native-comp-eln-load-path))))
                    port)